In the previous video, we have discussed about the half adder circuit. This video will be about full adder circuit. If you have missed our previous video you can find the link for the same in the description box below. One of the main drawback of half adder is its inability to add carry from the previous addition to the next bits. This is taken care using the full adder circuit. The full adder circuit consists of three input bits and two output bits. The three inputs to the full adder are A, B and Ci, where A and B are the bits to be added and Ci is the previous carry bit. The outputs are S and Co, where S is the Sum bit and Co is the carry bit generated for this sum. As seen here, let us consider this black box with 3 inputs as A, B and Ci and 2 outputs named as S and Co. The truth table for the full adder is also shown here. We can see that the output of sum is high whenever there are odd number of High Inputs.and Co bit is high if at least 2 or more than 2 inputs are HIgh. We will try to derive a Boolean equation for the outputs using K map. If you have doubt regarding K-map reduction, there is video link in the video description that might help you. Let us start by finding out what makes up the S bit. On performing reductions using K-map, we find that S is obtained by ex-oring A, B and Ci. Similarly let us try for Co bit. After performing reduction, Co is obtained as AB + BCi + ACi. Now since we have the Boolean expressions, we can build the adder circuit using Ex-or, OR and AND gates. We now have a clear understanding of what is actually inside the black box of full adder. Let us try implementing the circuit for full adder. As seen here the inputs A, B and Ci are connected to 3 input EX-or gate whose output is S bit. AB, BCi and ACi are connected separately to 3 AND gates and the output of these gates is connected to OR gate, whose output corresponds to Co. In this manner one can build a full adder using basic gates. However one does not need to build such a circuit to use full adder. Full Adder Integrated Circuits are available off the shelf which can be used for your applications. We hope that you have clearly understood the working of full adder circuit.
Video Lecture & Questions for Full Adder Video Lecture | Study Digital Electronics - Electrical Engineering (EE) | Best Video for Electrical Engineering (EE) - Electrical Engineering (EE) full syllabus preparation | Free video for Electrical Engineering (EE) exam to prepare for Digital Electronics.
Information about Full Adder
Here you can find the meaning of Full Adder defined & explained in the simplest way possible.
Besides explaining types of Full Adder theory, EduRev gives you an ample number of questions to practice Full Adder tests,
examples and also practice Electrical Engineering (EE) tests.